Battery case having surface-treated steel sheet

ABSTRACT

A battery case which has a high quality and is suitable for continuous forming and a surface-treated steel sheet which can be used suitably for manufacturing the battery case. The battery case is manufactured by forming, by the DI or DTR forming method, a surface-treated steel sheet obtained by plating the external and internal surfaces of an original steel sheet with a nickel-cobalt alloy. The nickel-cobalt alloy plated to both surfaces of the battery case can reduce the punching load in a cupping process, because the powdering property can be reduced remarkably. Therefore, the scratching of a die and a punch caused by metallic contact can be suppressed and the service lives of the die and the punch are prolonged, and then, the continuous productivity of the battery case can be improved. In addition, the case has a good lubricant retaining property, the removing property (stripping property) of the battery case which is an important factor for the DI or DTR formability can be improved.

FIELD OF THE INVENTION

The present invention concerns a container where alkaline solution ispacked.

More specifically, it concerns a battery exterior container of alkalimanganese batteries and the nickel cadmium batteries. Moreover, itconcerns the surface treated steel sheet that is suitable for makingthereof.

PRIOR ART

A method of barrel plating after press forming cold-rolled steel stripinto a battery container or a method of press forming nickel-platedsteel strip into a battery container have been adopted for manufacturinga battery container for such as alkali-manganese batteries and nickelcadmium batteries in which strong alkaline solution is packed. Thereason why nickel plating is used for batteries such as alkali manganesebatteries and nickel cadmium batteries is as follows. Nickel havingexcellent corrosion resistance to alkali is suitable for these batterieswhose electrolyte is chiefly strong alkaline potassium hydroxide.Moreover, nickel is suitable for batteries since nickel has steadycontact resistance when the battery is connected with an externalterminal. Furthermore, nickel has excellent spot welding properties incase where each component is spot welded when assembled into a batteryin the battery manufacturing process.

By the way, recently the main current of the plating method has beenpre-plating, in which a steel strip is nickeled beforehand, replacingpast barrel plating. It was difficult to manufacture products of highquality steadily by the past barrel plating because the difference ofthe plating thickness was large and it was especially difficult tonickel inside the container uniformly. As for pre-plating, the method ofgiving thermal diffusion processing after nickel plating has come to beapplied chiefly to improve corrosion resistance. Now, the relationbetween the battery performance of the alkali manganese battery and thepositive electrode container (battery container) is described hereafter.The said battery performance and the properties of the inside ofpositive electrode container are closely related. It is said that thelower the contact resistance between the inside of the positiveelectrode container and the positive electrode mix of the alkalimanganese battery (consisting of manganese dioxide as a positiveelectrode active material, graphite as a conductor, and potassiumhydroxide as electrolyte), the more excellent the battery performance.As for alkali manganese battery, the positive electrode mix and thepositive electrode container are in contact, and the positive electrodecontainer serves as not only a container of the battery but also as aconductor which transfers electrons.

Therefore, when the contact resistance between the positive electrodemix and the inner surface of the positive electrode container is great,the internal resistance of the battery rises. It causes decrease in theoperation voltage and in the electrical discharge duration, obstructingthe battery performance. So, it is desirable to decrease the contactresistance between the positive electrode mix and the inner surface ofthe positive electrode container. Therefore, roughing the surface innersurface the positive electrode container, making a ditch on the positiveelectrode container in the vertical direction, and applying conductivecoating or a conducting material made by adding binder to graphite areproposed to decrease the contact resistance between the positiveelectrode mix and the inner surface of the positive electrode container.

Next, the press-forming method of the battery container is described.

Recently, DI (drawing and ironing) forming method is increasingly usedas a method of thinning wall to increase the capacity of the batteryreplacing the past multi step deep drawing method (see PublishedJapanese Patent Hei 7-99686). This DI forming method and DTR (drawingthin and redraw) forming method is capable of increasing the batterycapacity because the container side wall being thinner than the bottomthickness allows more positive electrode and negative electrode activematerials to be contained. Moreover, the thick bottom has an advantageto improve the pressure resistance of the battery.

OBJECTIVE OF THE PRESENT INVENTION

By the way, although the DI forming method and the DTR forming methodare effective for increasing battery capacity as mentioned above, thereis a disadvantage when they are used for continuous forming because thedeformation resistance of the material in those methods is greater thanin the conventional multi step deep-drawing forming method. Concretely,when the powdering quality (powdery dropout of the plating layer) in thecupping process of the DI forming method and the DTR forming method isinferior, the powder adheres to the die and the punch in the ironingprocess causing a defect in the container side wall. Although thesimilar phenomenon happens in the deep-drawing forming, theabove-mentioned defect is more remarkable in the DI forming method andthe DTR forming method because the container wall has small surfaceroughness, which produced more lustrous appearance.

Moreover, powdering quality is more critical in the DI forming methodand the DTR forming method. Also, because the contact pressure of thematerial and the tool is greater in the DI forming method and the DTRforming method than that in the drawing method, favorable lubrication isrequested for tool life. Therefore, materials which have a favorablepowdering quality and retention of the press lubricant are requested.

When using nickel plated steel sheet, one of the ways to improve theretention of the lubricant is to cause cracks in the plating layer atthe press-forming step and to hold the lubricant in the part wherecracks are caused. As a means for this, gloss nickel plating producing ahard plating layer is generally brought to mind. However, although thegloss nickel plating produces a hard gloss plating layer, it is brittleand it has inferior powdering quality at the press-forming. In addition,since gloss plating involves organic additives containing sulfur (forexample, sulfomic acid having=C-SO₂ -group) to make electrolyticallydeposited crystal grains fine, sulfur is absorbed in the plating layer,which causes the embrittlement with sulfur promoted by the temperaturerise of the material in the ironing and the stretching process of the DIforming and the DTR forming resulting in a deteriorated powderingquality.

The inventor of the present invention examined various materials for abattery container having excellent formability in the DI forming methodand the DTR forming method from such viewpoints, and found thatnickel-cobalt alloy plating is suitable.

The present invention is based on such findings and it is aimed at abattery container having high quality and excellent continuousformability and a surface treated steel sheet which is suitable forproducing the said battery container. Another objective of the presentinvention is to improve the removability of container (strippability)after the DI forming and the DTR forming. This is taken intoconsideration since the difficulty of stripping the container from thepunch (strippability) in the final pressing process is critical in thecontainer manufacturing in addition to the above-mentioned powderingquality. At stripping where the container is pulled out from the punchhitching fingernails on the edge of the container, there was a problemthat an inferior stripping caused breaking and split at the open edgeportion of the container more frequently, which deteriorated theproductivity.

THE BEST MANNER REALIZING THE PRESENT INVENTION

The battery container as claimed in Claim 1 which achieves the abovementioned purpose is obtained by forming a surface treated steel sheet,of which inside and outside are plated with nickel-cobalt alloy, usingDI forming method or DTR forming method. The battery container asclaimed in Claim 2 is assumed to be the battery container as claimed inClaim 1 in which cobalt content of the above-mentioned nickel-cobaltalloy plating is from 0.5 to 10 percent by weight. The battery containerclaimed in Claim 3 is assumed to be the battery container as claimed inClaim 1 in which the thickness of the above-mentioned nickelcobalt-alloy plating is from 0.5 to 3 μm for the inside of the containerand from 1.0 to 4 μm for the outside of the container. The batterycontainer claimed in Claim 4 is obtained by forming a surface treatedsteel sheet, of which inside and outside are plated with nickel-ironalloy, using DI forming method or DTR forming method. The batterycontainer as claimed in Claim 5 is assumed to be the battery containeras claimed in Claim 4 in which the iron content of the above-mentionednickel-iron alloy plating is from 0.5 to 5 percent by weight. Thebattery container as claimed in Claim 6 is assumed to be the batterycontainer as claimed in Claim 5 in which the thickness of theabove-mentioned nickel-iron alloy plating is from 0.5 to 3 μm for theinside of the container and from 1.0 to 4 μm for the outside of thecontainer. The surface treated steel sheet as claimed in Claim 7 is madeby plating inside and outside a steel sheet with nickel-cobalt alloy.The surface treated steel sheet as claimed in Claim 8 is assumed to bethe surface treated steel sheet as claimed in Claim 7 in which thecobalt content of the above-mentioned nickel-cobalt alloy plating isfrom 0.5 to 10 percent by weight. The surface treated steel sheet asclaimed in Claim 9 is made by plating inside and outside a steel sheetwith nickel-iron alloy. The surface treated steel sheet as claimed inClaim 10 is assumed to be the surface treated steel sheet as claimed inClaim 9 in which iron content of the above-mentioned nickel-iron alloyplating is from 0.5 to 5 percent by weight.

EMBODIMENT

First of all, the formation of the nickel-cobalt alloy plating of theabove-mentioned battery container and the surface treated steel sheet isdescribed. When using a plating bath in which cobalt sulfate is added toWatts bath or sulfamate bath, eutectoid of cobalt and nickel is formed.As a result, with the increase of cobalt content in the plating layer,the hardness of the eutectoid plating layer increases.

Concretely, the surface hardness of the plating by the nickel sulfamatebath rises to about 300 to 320 (Vickers hardness) when cobalt is addedby 1 g/1 (cobalt content 5%), while it is about 220 to 230 (Vickershardness) when cobalt is not added.

Similarly, the hardness of the plating layer of the nickel-iron alloyplating reaches about 500 (Vickers hardness) when containing iron by 3to 5% in the nickel plating layer. Thus, the surface treated steel sheethaving hardened plating layer was manufactured, and then this surfacetreated steel sheet was formed into a battery container (alkalimanganese battery LR6 type) using the DI forming method and the DTRforming method, etc. And when the side wall inside and outside of thebattery container was observed with a microscope, a fine surfaceroughening was observed.

In order to examine the powdering quality, the lubricant inside andoutside of the manufactured battery container was removed with anorganic solvent and then the powder dropped out from the plating layerwas adhered to the adhesive tape and the amount was observed with themagnifying glass (magnification 25 times). As a result, remarkabledecrease in the powdering quality was observed.

In order to evaluate the continuous formability of the batterycontainer, powdering qualities in three kinds of forming methods, whichare the deep-drawing method, the DI forming method, and the DTR formingmethod, were examined. It was found that nickel-cobalt alloy coatedsteel sheet and nickel-iron alloy coated steel sheet which constitutethe surface treated steel sheet used in the present invention havesmaller-punching load compared to the ordinary gloss nickel plated steelsheet.

When the surface treated steel sheet of the present invention is formed,the punching load is small because the lubricant enters theabove-mentioned finely rugged surface of the surface treated steel sheetin the cupping process and the friction resistance decreases in thesubsequent ironing process of the DI forming and the stretching processof the DTR forming due to the favorable retention of the lubricantbetween the materials and the die or the punch. It is greatlyadvantageous that the defects of the die and the punch due tometal-to-metal contact decrease because of the lowered punching load,resulting in longer die life and improved continuous productivity of thebattery container. And favorable retention of the lubricant is alsoadvantageous for the removability (strippability) of the batterycontainer which is an important factor in the DI formability and the DTRformability.

The present invention is not only applied in the DI forming method andthe DTR forming method as a means to thin the wall of the batterycontainer, but also favorably applicable in the conventional multi stepdeep-drawing method because it improves the powdering quality anddecreases defects.

Moreover, when a battery is produced by forming the plated steel sheetof the present invention into an alkali manganese battery containerusing the DI forming method or the DTR forming method, the adhesion ofthe positive electrode mix to the inside of the container, and theadhesion of the graphite coating coated inside the battery container tothe positive electrode mix after formed into the battery container areimproved by the existence of the above-mentioned finely rugged surface.That is, the use of the plated steel sheet of the present inventioncompensates the drawbacks that the surface roughness inside thecontainer formed using the DI forming method and the DTR forming methodis small and that the adhesion of it to the positive electrode mix orthe graphite coating is inferior. Since the nickel-based alloy platingcontaining cobalt and iron of the present invention are involved in theiron-group which has excellent resistance to alkali corros ion anddissolution, it is a suitable material for the batteries such as thealkali manganese batteries, the nickel cadmium batteries, and the nickelhydrogen batteries of which electrolyte is high concentration alkalineline solution.

By the way, the suitable cobalt content of the nickel-cobalt alloyplating is from 0.5% to 10%. When the cobalt content is less than 0.5%,it is not effective for hardening the cobalt plating layer. On the otherhand, when the cobalt content is exceeding 10%, it is uneconomicalbecause the hardening effect on the surface treated steel sheet issaturated and also because cobalt is expensive precious metal.

As for the nickel-iron alloy plating, the suitable iron content is from0.5% to 5%. When the iron content is less than 0.5%, hardening effectcan not be obtained. On the other hand, when the iron content isexceeding 5%, the hardening effect is saturated, and it also causesdifficulty to control the bath when the iron content increases anyfurther. In relation to the plating thickness of the surface treatedsteel sheet of the present invention, the preferable range for theinside of the container is from 0.5 to 3.0 μm both for the nickel-cobaltalloy plating and the nickel-iron alloy plating. On the other hand, thepreferable range for the outside of it is from 1.0 to 4.0 μm.

When the plating thickness of inside the container is less than 0.5 μm,the exposure of the steel substrate is increased and the corrosionresistance is inferior in the container of batteries such as alkalimanganese battery, causing deterioration in the battery performance dueto dissolving out of the ferrous ion into the electrolyte. On the otherhand, when the plating thickness outside the container is less than 1.0μm, rust might be generated on the battery container during pressforming process and the battery manufacturing process and whilepreserving it for a long period of time since it does not have enoughcorrosion resistance.

The upper limits of the plating thicknesses inside and outside of thecontainer are 0.3 μm and 0.4 μm, respectively, because the effect issaturated when the plating thickness exceeds these values and also it isuneconomical to make them any thicker.

Usually a low carbon aluminum killed steel is suitably used a basematerial of a surface treated steel sheet.

In addition, cold-rolled steel strip prepared from non-aging hyper lowcarbon steel (carbon content is less than 0.01%) with niobium and/ortitanium added is also used. And the steel strip subjectedElectro-cleaning, annealing, and temper rolling after cold-rolling usinga conventional method is used as a substrate for plating. After that asurface treated steel sheet is manufactured by plating the steelsubstrate with nickel-cobalt alloy or nickel-iron alloy.

As for the plating bath, however both of the known sulphate bath and thesulfamate bath can be used, sulfamate bath is suitable since it iscomparatively easy to be controlled. Since either ratio of cobalt oriron to nickel deposited into plating layer is several times greaterthan that of concentration in either plating bath, it is possible to usenickel anode for anode and to supply cobalt and ferrous ions in the formof sulfamate or sulfate.

EXAMPLE

The present invention is explained more concretely referring to thefollowing examples.

Low carbon aluminum killed steel sheets subjected to cold-rolling,annealing, and temper rolling having the thickness of 0.25 mm and 0.4 mmwere used as the substrates for plating. The chemical compositions ofboth steel substrates were as follows. C:0.04% (% means percent byweight, same for the following), Mn:0.22%, Si:0.01%, P:0.012%, S:0.006%,Al:0.048%, N:0.0025%.

After subjected to the ordinary pretreatment comprising alkalielectrolytical degreasing, rinsing, acid sulfuric dipping into andsubsequent rinsing, the above-mentioned steel substrates were platedwith nickel-cobalt alloy and nickel-iron alloy on the followingconditions and made into surface treated steel sheets.

1) Nickel-cobalt alloy plating: Various quantity of cobalt sulfate wereadded to nickel sulfamate bath to have the nickel plating layer containcobalt.

    ______________________________________                                        Bath composition:                                                             ______________________________________                                        nickel sulfamate                                                                            Ni(NH.sub.2 SO.sub.3).4H.sub.2 O                                                             600    g/l                                         nickel chloride NiCl.sub.2.6H.sub.2 O 10 g/l                                  cobalt sulfate CoSO.sub.4.6H.sub.2 O 5-20 g/l                                 boric acid H.sub.3 BO.sub.3 40 g/l                                            citric acid  0.6 g/l                                                          saccharin  0.5 g/l                                                          ______________________________________                                    

Bath pH=4 (adjusted with addition of the sulfamic acid), stirring: airstirred. Bath temperature 60° C. Cathode current density 10 A/dm².Anode=A titanium basket packed with S pellet (brand name made by theINCO company, spheroidal) and covered with a bag made of polypropylenewas used as anode. The cobalt content and the thickness of the platingfilm were varied by changing the amount of adding cobalt sulfate and theelectrolysis duration on the above-mentioned conditions.

2) Nickel-iron alloy plating: Iron sulfamate was added to the nickelsulfamate bath to have the nickel plating layer contain iron.

    ______________________________________                                        Bath composition:                                                             ______________________________________                                        nickel sulfamate                                                                            Ni(NH.sub.2 SO.sub.3).4H.sub.2 O                                                             450    g/l                                         iron sulfamate Fe(NH.sub.2 SO.sub.3).5H.sub.2 O 0-7 g/l                       boric acid H.sub.3 BO.sub.3 45 g/l                                            citric acid  0.6 g/l                                                          saccharin  0.5 g/l                                                          ______________________________________                                    

Bath temperature=50° C., Cathode current density=10 A/dm²,

Anode: A titanium basket packed with S pellet (brand name made by theINCO company, spheroidal) and covered with a bag made of polypropylenewas used.

The amount of iron content and the thickness of the plating film werevaried by changing the amount of adding iron sulfamate and theelectrolysis duration on the above-mentioned conditions. After theabove-mentioned nickel-cobalt alloy plating and the nickel-iron alloyplating were done, the plating layer was dissolved to 3% nitric acid andthe plating thickness and the alloy composition of the plating film wereanalyzed with ICP (inductively coupled plasma atomic emissionspectrochemical analysis) method.

The plating thickness (μm) was determined by dividing the dissolvedamount value of each element with the value of the plated area andconsidering the specific gravity of each element. Table 1 shows thoseresults.

(Battery container manufacturing)

As for the battery container formed by the DI forming method, theabove-mentioned plated steel sheet having the thickness of 0.4 mm waspunched out into a blank 41 mm in diameter, drawn into a cup 20.5 mm indiameter, and then formed into 13.8 mm in outside diameter, 0.20 mm incontainer wall thickness and 56 mm in height by redrawing and two-stepironing using DI forming machine. Finally, the upper part was trimmedoff to shape a LR6 type battery container 49.3 mm in height. On theother hand, as for the battery container formed by the DTR formingmethod, the plated steel sheet 0.25 mm in sheet thickness was punchedout into a blank 58 mm in diameter, and then shaped into a LR typebattery container 13.8 mm in outside diameter, 0.20 mm in container wallthickness and 49.3 mm in height by several times of drawing andredrawing.

(Evaluation of the powdering quality)

The powdering quality was evaluated by the decrease in weight afterforming in the manufacturing process of the above-mentioned batterycontainer. The process was comprising blanking→cupping→degreasing→weightmeasurement (1)→forming→degreasing →weight measurement (2). Degreasingwas conducted by alkali dipping degreasing followed by ultrasoniccleaning in acetone.

Since the error might be large if the weight decrease was measured everyone container, 30 of them as one measurement unit were repeated threetimes. Table 1 shows the result. As is apparent in Table 1, while in thecomparative example 1 and 2, a large number of powders dropout from thecontainers (from 74 to 160 mg/30 containers), in this present inventionsexample of 1 to 10, a small number of powders dropout (from 23 to 33/(30containers)). This shows that the battery container of the presentinvention is excellent in powdering.

SURFACE HARDNESS OF THE PLATING LAYER

The surface hardness of the plating layer of the samples obtained in theexamples and the comparative examples were measured using the Vickershardness testing machine (load: 5 g). Table 1 shows the result. As isapparent in Table 1, the plating layer surface hardness of bothcomparative example 1 and 2 are low, while the plating layer surfacehardness of the examples of the present invention 1 to 10 is high. Thisshows that the plating given to the surface treated steel sheet used forthe battery container of the present invention has enough surfacehardness for a battery container.

STRIPPABILITY

Strippability in the DI forming was measured as follows.

The stripping load required when pulling out the container from thepunch by returning the punch after ironing process was measured with aload cell installed in the punch. As shown in Table 1, the strippingload of each example of this invention is less than 50 kg, while thoseof comparative examples exceed 100 kg. This shows that the stripabilityof the battery container of the present invention is excellent.

                                      TABLE 1                                     __________________________________________________________________________                                     Forming    Hardness                               Alloy method Powdering of Strippability                                    Sheet Outside Plating Composition of quality plating (Stripping                                                               thickness or thickness                                                       (weight %) battery                                                            (mg/30 surface load)                      (mm) Inside                                                                            (μm)                                                                            Co Fe container                                                                          containers)                                                                         (Hv 5 kg)                                                                          (kg)                         __________________________________________________________________________    Example                                                                             1  Ni--Co                                                                            0.40 Outside                                                                           2.0  5.6                                                                              -- DI   26    395  35                               alloy  Inside 2.1 5.0 -- forming                                              plating                                                                      2 Ni--Co 0.25 Outside 1.1 0.6 -- DTR 23 345 39                                 alloy  Inside 0.6 0.5 -- forming                                              plating                                                                      3 Ni--Co 0.40 Outside 1.2 9.8 -- DI 27 390 25                                  alloy  Inside 0.5 9.5 -- forming                                              plating                                                                      4 Ni--Co 0.25 Outside 3.8 0.7 -- DTR 30 340 45                                 alloy  Inside 3.0 0.6 -- forming                                              plating                                                                      5 Ni--Co 0.40 Outside 3.9 9.6 -- DI 32 410 24                                  alloy  Inside 2.9 9.7 -- forming                                              plating                                                                      6 Ni--Fe 0.40 Outside 1.8 -- 13.0 DI 27 455 30                                 alloy  Inside 1.9 -- 11.3 forming                                             plating                                                                      7 Ni--Fe 0.25 Outside 1.0 --  1.2 DTR 24 405 43                                alloy  Inside 0.6 --  1.1 forming                                             plating                                                                      8 Ni--Fe 0.40 Outside 1.2 -- 28.9 DI 28 490 25                                 alloy  Inside 0.6 -- 27.5 forming                                             plating                                                                      9 Ni--Fe 0.25 Outside 3.8 --  1.3 DTR 23 410 46                                alloy  Inside 2.9 --  1.1 forming                                             plating                                                                      10  Ni--Fe 0.40 Outside 3.6 -- 29.2 DI 33 480 28                               alloy  Inside 2.8 -- 29.8 forming                                             plating                                                                     Comparative 1 Dull Ni 0.40 Outside 2.1 -- -- DI 115  220 115                  Example  plating  Inside 2.0 -- -- forming                                     2 Gloss 0.40 Outside 1.8 -- -- DI 160  490 118                                 Ni  Inside 1.9 -- -- forming                                                  plating                                                                   __________________________________________________________________________

EFFECT OF THE INVENTION

The battery container as claimed in Claim 1 is obtained by formingsurface treated steel sheet, which is made by plating inside and outsidethe substrate of steel sheet with nickel-cobalt alloy, using DI formingmethod or DTR forming method. Since the powdering is remarkablydecreased in the nickel-cobalt alloy plating, the punching load can belowered in the cupping process. Therefore, generation of defects of thedie and the punch due to metal-to metal contact is reduced, resulting inlonger die life and improved continuous productivity of the batterycontainer. Moreover, favorable retention of the lubricant improves theremovability of the battery container (strippability) which is animportant factor in the DI formability and the DTR formability.

The cobalt content contained in the nickel-cobalt alloy plating of thebattery container as claimed in Claim 2 is from 0.5 to 10 percent byweight. This enables to fully harden the nickel-cobalt alloy platinginside and outside of the battery container while considering theeconomy.

The thickness of the nickel-cobalt alloy plating of the batterycontainer as claimed in Claim 3 is from 0.5 to 3 μm for the inside of itand from 1.0 to 4 μm for the outside of it. So, deterioration in thebattery performance due to the ferrous ion solve-out into theelectrolyte resulted from corrosion at the exposed portion of the steelsubstrate can be surely prevented. At the same time, it enables tosmoothly conduct the press working of the battery container and tosurely prevent the rust generation while preserving the container for along period of time.

The battery container as claimed in Claim 4 is obtained by forming thesurface treated steel sheet, which is prepared by plating inside andoutside of the steel substrate with nickel-iron alloy, using the DIforming method or the DTR forming method. Since powdering can beremarkably decreased in the nickel-iron alloy plating as well as in thenickel-cobalt alloy plating, the punch load can be lowered in thecupping process. This enables to reduce the generation of defects of thedie and the punch due to metal-to metal contact, resulting in longer dielife and improved continuous productivity of the battery container.Moreover, favorable retention of the lubricant improves removability ofthe battery container (strippability) which is an important factor inthe DI formability and the DTR formability.

The iron content of the nickel-iron alloy plating of the batterycontainer as claimed in Claim 5 is from 0.5 to 5 percent by weight. Thisenables to fully harden the nickel-iron alloy plating inside and outsideof the battery container as well as to control the bath steadily whileconsidering the economy.

The thickness of the nickel-iron alloy plating of the battery containeras claimed in Claim 6 is from 0.5 to 3 μm for the inside of thecontainer. On the other hand, it is from 1.0 to 4 μm for the outside ofit. As a result, deterioration in the battery performance due to theferrous ion solve-out into the electrolyte resulted from corrosion atthe exposed portion of the steel substrate can be surely prevented. Italso enables to smoothly conduct the press working of the batterycontainer and to surely prevent the rust generation while preserving thecontainer for a long period of time.

The surface treated steel sheet as claimed in Claim 7 is a suitablematerial for the battery container as claimed in Claim 1, since thenickel-cobalt alloy plating is given to the inside and outside of thesubstrate.

The cobalt content of the nickel-cobalt alloy plating of the surfacetreated steel sheet as claimed in Claim 8 is from 0.5 to 10 percent byweight. This surface treated steel sheet enables to fully harden thenickel-cobalt alloy plating inside and outside of the battery containerwhen the it is manufactured into a battery container while consideringthe economy.

The surface treated steel sheet as claimed in Claim 9 is a suitablematerial for the battery container as claimed in Claim 4 since thenickel-iron alloy plating is given to the inside and outside of thesteel substrate.

The iron content of the nickel-iron alloy plating of the surface treatedsteel sheet as claimed in Claim 10 is from 0.5 to 5 percent by weight.This surface treated steel sheet enables to fully harden the nickel-ironalloy plating inside and outside of the battery container as well as tocontrol the bath steadily when it is manufactured into a batterycontainer while considering the economy.

What is claimed is:
 1. A battery container obtained by forming a surfacetreated steel sheet of which both inside and outside surfaces thereofare plated with a nickel-cobalt alloy using DI forming method or DTRforming method.
 2. The battery container as claimed in claim 1, in whichthe cobalt content of the said nickel-cobalt alloy plating is from 0.5to 10 percent by weight.
 3. The battery container as claimed in claim 1,in which the thickness of the said nickel-cobalt alloy plating is from0.5 to 3 μm for the inside surface of the container and from 1.0 to 4 μmfor the outside surface of the container.